New York : Researchers have found that Serotonin, a chemical known for encouraging happiness and well-being, can reduce the ability of some intestinal pathogens to cause deadly infections. The findings, publishing in the journal Cell Host & Microbe, could offer a new way to fight infections for which few truly effective treatments currently exist. "Although the vast majority of research on serotonin has centred on its effects in the brain, about 90 per cent of this neurotransmitter - a chemical that nerve cells use to communicate with each other - is produced in the gastrointestinal tract, study lead author Vanessa Sperandio from UT Southwestern Medical Centre in the US, explained. In humans, trillions of bacteria live within this space. Most of these gut bacteria are beneficial, but pathogenic bacteria can also colonize the gastrointestinal tract, causing serious and potentially fatal infections. Because gut bacteria are significantly affected by their environment, the research team wondered whether the serotonin produced in the gut can affect the virulence of pathogenic bacteria that infect the gastrointestinal tract. They worked with Escherichia coli O157, a species of bacteria that causes periodic outbreaks of often deadly foodborne infection. The team grew these pathogenic bacteria in Petri dishes in the lab, then exposed them to serotonin. Gene expression tests showed that serotonin significantly reduced the expression of a group of genes that these bacteria use to cause infections. Additional experiments using human cells showed that the bacteria could no longer cause infection-associated lesions on the cells if these bacteria were exposed to serotonin. Next, the researchers examined how serotonin affected virulence in living hosts. Using mice, the researchers studied how serotonin might change the ability for Citrobacter rodentium - a mouse gut bacterium often used as an analog for E. coli in humans - to infect and sicken their hosts. These mice were genetically modified to either over- or underproduce serotonin in their gastrointestinal tracts. Those that overproduced this neurotransmitter were less likely to become colonised by C. rodentium after being exposed to this bacterium or had relatively minor courses of illness, according to the study Treating mice with fluoxetine (sold under the brand name Prozac) to increase serotonin levels prevented them from getting sick from C. rodentium exposure. However, the mice that underproduced serotonin became much sicker after bacterial exposure, often dying from their illness. In the future, the research team plan to study the feasibility of manipulating serotonin levels as a way of fighting bacterial infections in the gastrointestinal tract.